Larger rotary lawnmowers sometimes employ multiple blades or decks. Usually the blades are rotated by belts and pulleys or shaft and gear drive mechanisms powered by a single gasoline or diesel engine. Other systems employ a single hydraulic motor for each blade. This eliminates most of the mechanical components and simplifies the system considerably.
Hydraulic motors employed in such systems typically are vertically oriented, with the motor being mounted on a spindle housing deck and an output shaft on the motor extending vertically through the deck to be connected directly or indirectly with a horizontal blade.
Rotary mower blades and hence the motors that drive them are subjected to considerable stress during operation. Motors and spindles are required to run for a long period of time without requiring service, and both are subjected to unbalanced loads. Motors and spindles are also subjected to shock loads when the blades strike hidden objects and the like. Testing for such drive systems includes longevity, unbalanced loads, and a shock load, sometimes referred to as a stake test, wherein the motor/blade is stopped suddenly by direct contact with a fixed stake.
A characteristic of a hydraulic motor is that the size and cost of the motor is generally related more or less directly with the diameter of the output shaft of the motor. For a hydraulic motor to drive a rotary blade directly while still passing the necessary unbalanced load and shock tests, it is necessary to employ a hydraulic motor having an output shaft having a relatively large diameter. This in turn requires a larger hydraulic motor, reducing system efficiency and increasing the cost of the system substantially.
In order to overcome this problem, and for other reasons, it is customary to connect a hydraulic motor with a rotary mower blade by means of a spindle assembly, wherein a larger diameter spindle extends between the hydraulic motor output shaft and the blade, with the blade being mounted on the spindle. The spindle, in such a situation, is mounted in a spindle housing and is suspended in suitable bearings for rotation in the housing. In testing, it has been found that when ball or roller bearings are used, shock loads cause impact hardening of the bearings and result in premature failure. To overcome this problem, some spindle assemblies employ plain bearing inserts or bushings instead of ball or roller bearings. Such bushings often employ so-called xe2x80x9ctop hatxe2x80x9d (flanged) bearings, which incorporate a thrust bearing on an end of the bushing. The bushings are lubricated by oil (hydraulic fluid) from the hydraulic motor, with the output shaft seal of the hydraulic motor being removed to permit oil transfer from the hydraulic motor to the spindle assembly. The spindle assemblies work adequately but are at the present time complicated and expensive and are generally designed to be an integral part of a particular brand of hydraulic motor. Also, serious oil leakage can occur if a spindle seal fails in such a device. The oil can destroy a considerable amount of fine turf on a golf course or the like before the seal failure is noted.
An object of the present invention is to provide a simpler, less expensive spindle assembly for a hydraulic motor, wherein the spindle assembly can be fitted to virtually any brand of hydraulic motor and the likelihood of substantial undetected oil leakage is reduced.
In accordance with the present invention, a spindle assembly for a rotary mower operated by a hydraulic motor comprises a spindle that is drivingly connected between an output shaft of a hydraulic motor and a horizontal blade assembly, and a spindle housing that rotatably supports the spindle for rotation and thrust loads. The spindle housing (or body) is formed of an aluminum alloy. A bore in the housing fits closely over the spindle and serves as a plain bearing for rotatably supporting the spindle. The spindle assembly functions adequately without any bearing inserts between the housing and the spindle, although bearing inserts at the ends or at least the lower end of the spindle can be employed in order to achieve higher load bearing capabilities. The spindle of the present invention is formed from conventional rod stock and is machined to produce an upper end of reduced diameter.
An impeller and thrust washer (which can serve as an impeller or thrust washer or both) fits on a narrower upper end of the spindle and is held in place by a tapered snap ring (also called a circlip) that fits in a tapered groove in the spindle. The tapered groove causes the tapered snap ring to tightly hold the washer in place so it is urged to rotate with the spindle. Radial grooves are formed on at least a lower side of the washer and preferably on both sides. These assist to impel or pump oil or hydraulic fluid outwardly as the washer rotates.
In one aspect of the invention, an oil circulation channel is formed in the housing so as to extend from a position adjacent the outer edge of the impeller washer downwardly and inwardly to a lower end of the spindle housing adjacent the spindle. Oil received downwardly from the hydraulic motor flows outwardly over the outer edges of the impeller washer. The oil then flows downwardly through the oil circulation channel to the junction of the spindle and spindle housing at the lower end of the spindle housing and then flows upwardly between the spindle housing and the shaft to the upper end of the shaft. There, the oil is impelled outwardly by the washer. This forces the oil to recirculate downwardly through circulation channels and then up across the bearings. The grooved impeller washer thus serves as a pump for recirculating oil across the bearing surfaces in the spindle assembly. The output shaft seal of the hydraulic motor is removed in this embodiment, so the spindle assembly is lubricated by motor fluid.
The spindle assembly is formed of aluminum, preferably an aluminum alloy such as the 850 series or 356 series. Other materials having comparable characteristics and which could serve as a plain bearing material with the spindle material employed could be used. The bore in the spindle assembly is designed to fit relatively closely to the spindle, so that the spindle housing more effectively resists side loads and unbalanced loads to which the spindle may be subjected. A diametral clearance of approximately 0.001 inch is desirable. A clearance of 0.0005 to 0.002 inches is satisfactory. More tolerance is permissible if bearing inserts are used.
Upward and downward axial thrust loads are resisted by the impeller and thrust washer acting against the bottom of the spindle housing pilot bore and the face of the motor pilot. The coupling between the spindle and the motor output shaft allows sufficient axial movement of the washer to permit the washer to resist thrust loads.
In another aspect of the invention, case drain oil pressure is used to circulate oil through the spindle assembly. The invention also contemplates that the hydraulic motor output shaft can remain sealed and a separate reservoir can be employed to provide lubricant for the spindle assembly. The separate reservoir can be incorporated in the motor or be separate from the motor, or a separate lubrication block can be positioned between the motor and the spindle assembly. A fluid outlet between a pair of spaced motor output shaft seals can be used to provide a visible indication of motor oil seal failure.
With the foregoing spindle assembly, manufacturing costs are dramatically reduced, while the life and effectiveness of the spindle assembly are maintained. Expensive bearing inserts are eliminated, and expensive machining operations are eliminated. Also, virtually any brand of hydraulic motor that can be offered in DIN standard configuration can be fitted to this spindle assembly.
These and other advantages and features of the present invention are described in detail below and shown in the appended drawings.